Scientists have long understood the role of the element iron in sustaining the earth’s magnetic field. Iron is the critical element — the motion of liquid iron in the earth’s outer core generates the field.
“Our planet accreted from rocky material that surrounded our Sun in its youth, and over time the most-dense stuff, iron, sank inward, creating the layers that we know exist today–core, mantle, and crust. Currently, the inner core is solid iron, with some other materials that were dragged along down during this layering process. The outer core is a liquid iron alloy, and its motion gives rise to the magnetic field.”
Scientists were less certain about how the magnetic field was first created and then sustained throughout Earth’s history– until now.
A team led by Carnegie’s Alexander Goncharov published new research in Nature that sheds light on how this geological phenomenon developed and evolved over time.
Goncharov and his team knew that to understand the earth’s magnetic field, they would need to explore the way that heat is conducted by the solid inner core and the liquid outer core of the earth, which are both largely made up of iron.
It would be impossible to reach anywhere near the earth’s core and take samples, so the researchers recreated the conditions in the lab.
“We sensed a pressing need for direct thermal conductivity measurements of core materials under conditions relevant to the core. Because, of course, it is impossible for us to reach anywhere close to Earth’s core and take samples for ourselves.”
Science News notes that” the materials obviously exist under very extreme conditions, both very high temperatures and very intense pressures.”
To mimic planetary core conditions as closely as possible, Goncharov and his team heated a diamond anvil cell with a laser and studied how iron conducts heat in it. Tiny samples of material were squeezed between the two diamonds in the cell, recreating the extreme conditions deep in the earth’s core.
By studying how the iron samples transmit heat, the researchers were able to state with confidence which of the estimates previously made by other scientists about earth core thermal conductivity were the most accurate. The team announced that conductivity in the earth’s core is likely to be at the lower end of previous estimates — between 18 and 44 watts per meter per kelvin.
Scientists were able to deduce that the energy necessary to sustain the moving liquid in the earth’s outer core, or “geodynamo,” has been available since very early in the history of Earth.
The investigation is not over yet — researchers will now need to study how the other elements would have behaved when they came “along for the ride” with the mass of molten iron.
“In order to better understand core heat conductivity, we will next need to tackle how the non-iron materials that went along for the ride when iron sunk to the core affect these thermal processes inside of our planet.”
Other external factors may play a role in sustaining the field. Separate research released earlier this year concluded that the moon plays a role in sustaining the earth’s magnetic field, reports Science News.
“Since neither the Earth’s rotation around its axis, nor the direction of its axis, nor the Moon’s orbit are perfectly regular, their combined effect on motion in the core is unstable and can cause fluctuations in the geodynamo…. The Earth continuously receives 3,700 billion watts of power through the transfer of the gravitational and rotational energy of the Earth-Moon-Sun system, and over 1,000 billion watts is thought to be available to bring about this type of motion in the outer core.”
A lot of energy due to gravitational effects generated by the earth-sun-moon system is available to keep the molten iron in the earth’s core moving, thus sustaining the magnetic field.
The movement of the ocean tides with the moon is familiar to most people. Researchers claim that a parallel process is responsible for deforming the earth’s mantle and moving the liquid iron alloy inside the core.
“The Earth has a slightly flattened shape and rotates about an inclined axis that wobbles around the poles. Its mantle deforms elastically due to tidal effects caused by the Moon. The researchers show that this effect could continuously stimulate the motion of the liquid iron alloy making up the outer core, and in return generate Earth’s magnetic field.”
The moon may play a part in sustaining the earth’s magnetic field, but is the field going to be sustained at current levels forever?
Another research paper released this year found that the strength of the earth’s magnetic field may be decreasing, and the poles may be preparing to flip.
Science World Reportreports that “[o]ver the past decades, it has become clear that the invisible bubble that protects our planet from outer space’s harsh conditions is getting weaker. As per the approximate estimates by scientists, Earth’s magnetic field is getting weaker by around 10 times [more] than previously thought, which implies that the planet is losing around five percent of its strength every 10 years.”
Researchers stress that flips in the poles, and changes in the field itself, have occurred periodically throughout the earth’s history and there is no evidence that any effect destructive to humans will result.
“Researchers suggest that the magnetic poles are gearing up to flip, a phenomena that takes place once every 100,000 years. However, according to experts, there is no reason to worry on hearing about such a possibility because until date there has been no proof that life on Earth suffered in the past, when such an event took place. The consequence, of the phenomena, could simply mean that a compass could eventually point south in place of north.”
The flip will occur as a consequence of changes in the motion of the same molten iron that is moving deep in the earth’s core.
[Image via NASA/Apollo17 CrewWikimedia Commons/Public Domain]